1. Field of the Invention
This invention relates to protective carrying cases for drill bits. More particularly, the invention relates to cases adapted to holding a number of drill bits in a secure manner to protect the drill bits against damage during transportation or storage.
2. Description of Background Art
Drill bits, or "drills" as they are referred to by many of their industrial users, are employed in a wide range of manufacturing industries. One particular industry which uses drills very extensively is the printed circuit board manufacturing industry.
Printed circuit boards are used in an extremely wide variety of electronic and electrical equipment in the consumer, commercial, industrial and military markets. To a large extent, planar conductors on the surfaces of printed circuit boards have replaced wires which were formerly used to interconnect different points in an electrical or electronic circuit. Typically, the first step in manufacturing printed circuit boards is to adhere a copper sheet onto one or both sides of a thin, flat "board" made of insulating plastic or fibreglass. Holes are then drilled through the board as is explained below. The copper sheet is then coated with a light-sensitive emulsion. Next, a photographic negative defining desired conductive paths is placed in contact with the emulsion coated copper sheet, and the whole exposed to light. This process results in a physical change in the emulsion, making it acid resistant where conductive paths have been delineated by differing amounts of light received through the negative. When the exposed board is subsequently dipped in an acidic etching bath, those portions of the copper sheet other than the conductive paths are selectively etched away, leaving a pattern of conductive paths consisting of thin strips of copper sheet adhered to the surface of the board.
As was mentioned above, holes must be drilled through the printed circuit board at the end of each conductive path. The holes are adapted to receive the wire leads from electronic components such as resistors, capacitors, transistors and the like, which are to be mounted to the board. At least two separate holes are required for each electronic component to be mounted on the printed circuit board. Each printed circuit board may have dozens or hundreds of components. Also, electronic components such as integrated circuits may have up to several dozen leads, each requiring a hole in the printed circuit board. Therefore, manufacture of printed circuit boards typically requires the drilling of several hundred or a thousand or more holes of a variety of sizes in just a single printed circuit board.
Every printed circuit board has at least one layer of copper sheet and one layer of insulating board material which must be penetrated during drilling. Frequently, the insulating board material is fibreglass-reinforced epoxy. Since those materials which printed circuit board drills must penetrate are typically hard and abrasive, the drills used must be very hard to ensure an acceptably long life for the drills. Accordingly, most printed circuit drills are tipped with tungsten carbide, which is one of the hardest and most wear resistant materials available for industrial use.
Generally, materials which are very hard are inherently brittle. This is true of tungsten carbide, with the harder grades being more brittle than softer grades. Printed circuit board (PCB) drills, then, which are tipped with tungsten carbide, are readily susceptible to chipping and breaking of the cutting edges of the drill if not handled carefully.
Typically, PCB drills are fitted with an annular collar interference fitted on the shank of the drill a measured distance from the point. Contact of the collar with the drill machine collet, controls the depth of drill penetration. Now since PCB drills are used to penetrate highly abrasive materials, the drills wear rapidly inspite of the extremely hard materials used on their cutting edges. For that reason, PCB drills are repointed up to three or more times before they are finally discarded. To be repointed, the drills must be removed from drill spindles, and transported to a repointing machine. Many of the repointing machines require removal of the annular shank rings before they can be repointed. This necessitates separate removal and replacement steps in conjunction with the repointing operations. When worn drills are placed helter skelter in a box for transport to a repointing machine, chipping of contacting drills often occurs.
Because of the potential for damage which can occur to PCB drills during transport, a variety of protective carrying cases intended to minimize damage to the drills have been devised.
One type of carrying case presently used has a block of resilient material such as styrofoam containing a plurality of parallel cylindrical holes. The diameter of the holes in the styrofoam are slightly smaller than the shank diameters of drills which the block is intended to accommodate. Thus, drills which are inserted shank-first into the holes are held in place by an interference fit. A disadvantage of this type of drill carrying case is that it is difficult to selectively remove a drill from the box without striking and thereby damaging an adjacent drill. Further, this type of packaging does not allow all the drill points to settle at the same height; incoming drill bit inspection is therefore difficult.
A second type drill carrying case consists of a plastic tube and end cap. With this method, drills are packaged individually.
Another type of package consists of a vacuum formed pack with cavities that approximate the shape of the drill. Each cavity accommodates 1 drill.
A third type of drill carrying case in current use has the general external shape of a thin, flat, rectangular box. The top and bottom of the box are hinged at the back, and the facing front edges of the box provided with a fastener which may be readily joined and separated. When unfastened, the top of the box is foldable backwards, placing both top and bottom of the box in a common horizontal plane. Extending perpendicularly upward from the inner surface of the back hinged surface of the box is a thin holding block spanning nearly the full width of the box. The holding block contains a plurality (twelve or so) of parallel blind holes adapted to loosely hold the shanks of drills. Foam rubber strips fastened to inner facing surfaces of the top and bottom panels of the box span the width of the box. When the top and bottom panels of the box are snapped together, compressive pressure of the resilient foam rubber strips upon the drills holds them in place. A disadvantage of this type of drill carrying case is the limited range of drill sizes which may be carried in a given case. The practical limit in this range is from about #97 drills (0.0059 inch) to 1/8" diameter drills. To accommodate drills from 1/8" to 1/4", excessively thick foam rubber strips would be required. If the smaller thickness strips, adequate for use with smaller diameter drills were used with the larger size range drills, the excessive percentage of foam thickness depression caused by the larger diameter drills would destroy the elastic memory of the foam strips.
The present invention was conceived of to overcome some of the disadvantages of existing drill carrying cases.